日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Mono-dispersed MFI-type zeolite nanocrystals with a diameter of 80～150 nm were successfully prepared in water-surfactant-oil solution. It was found that the ionicity of the surfactants used in preparation affected the crystallinity and structure of the silicalite crystals. When using ionic surfactants, amorphous SiO₂ or the coexistence of silicalite crystals and amorphous SiO₂ was revealed from SEM observation, which was confirmed by X-ray diffraction analysis. On the contrary, when using a nonionic surfactant, the X-ray diffraction patterns of the sample showed peaks corresponding to pentasil-type zeolite, and silicalite nanocrystals with a diameter of approximately 60 nm could be obtained. Since the aggregation of the silicalite nuclei was inhibited by the adsorbed surfactants on the surface during hydrothermal treatment, mono-dispersed nanocrystals could be prepared. In order to evaluate the surface crystallinity of the nanocrystal, the Raman spectrum of the nanocrystal was measured. The spectrum of the nanocrystal showed peaks around 380 cm⁻¹, 430 cm⁻¹ and 470 cm⁻¹, which corresponded to the five-, six- and four-membered rings, respectively, indicating that the surfaces of the nanocrystals with a diameter of approximately 60 nm was well-crystallized without amorphous SiO₂. By adding an Al source into the synthetic solution, ZSM-5 type zeolite nanocrystals with strong acid sites could be obtained.